The current model of the primary auxin response is based largely on recent findings regarding the mechanism of auxin perception, on in vitro studies of DNA binding by Auxin Response Factors (ARF proteins), and on auxin-responsive gene expression data. The defining features of auxin-responsive promoters are very poorly understood, and the determinants of specificity guiding in vivo ARF-promoter interactions have not been investigated. Addressing these questions is a critical next step in understanding the primary auxin response and substantiating the model of auxin action in transcription. The results of the proposed studies will be of broad utility to studies of hormone responses in plants and animals, and will be of particular relevance to studies of plant growth and development. With the experiments presented in this proposal, I aim to 1) identify ARF target loci through analysis of auxin-responsive gene expression and Chromatin Immunoprecipitation (ChIP) with the transcription factors MP/ARF5 and NPH4/ARF7;2) define MP/ARF5- and NPH4/ARF7-recruiting promoters through consolidation and comparative bioinformatics analysis of new and existing datasets;3) define determinants of specificity in ARF protein-promoter interactions using quantitative promoter-reporter assays and analysis of DNA sequences coimmunoprecipitating with truncated and chimeric ARF proteins